Precision cutting of large stones is efficiently achieved using a continuous cable imbedded with diamond-impregnated beads. The cutting cable, generally referred to as a “diamond wire,” is drawn between two wire guide wheels, which are positioned to accommodate the wire's travel across a particular span of space. In this way, the stone to be cut is introduced into the span and into contact with the wire as it quickly travels between the wire guide wheels. As the wire travels, it comes into contact with the stone, and cuts into the slab.
The systems involving a tensioned wire spanning between two wire guide wheels are quite common in the quarrying and saw shop stone cutting industries. Such unguided, cutting wire systems are preferred to bar-guided belts and wires or cutting wheel systems because the unguided, cutting wire systems offer relative simplicity, a capacity for larger cut spans, higher cutting rates, reduced maintenance, and lower capital costs. However, the unguided, cutting wire systems generally suffer from a lower level of cutting precision as compared to the other cutting systems.
In the unguided, cutting wire systems, the “diamond wire” must be held under tension so that the wire will align itself in a straight line between the wire guide wheels. The tension is required in order to achieve the precision of a straight cut. Specifically, the wire must be kept under tension sufficient to eliminate sagging of the wire across the span. Generally, the greater the span distance, the higher the tension under which the wire must operate in order to maintain a stable, straight cut.
Optimal cutting rates and optimal cutting wire draw speeds are generally specified by the diamond wire manufacturer, who takes into consideration such factors as the geometry and material of the cutting surface, the hardness of the stone to be cut, and target tool pressures. Wire draw speeds are generally regulated by motor speed controllers, which monitor operation conditions and compensate for changing operational loads.
During operation of an unguided, cutting wire system, adding cutting loads will elastically stretch the cutting wire, which reduces the precision of the cut. When the tool pressures on the wire are high while the wire is already under tension, the wire will somewhat deform. As long as the total pressure on the wire pressure is within the wire's elastic range, the deformation will be only temporary. On the other hand, when the tension on an unloaded wire is already near the wire's elastic limit, applying tool pressure to the wire commonly brings the total pressure on the wire to a level that exceeds the wire's elastic yield point, which leads to permanent and undesirable deformation of the wire due to the tensile stretching.
Assuming the tensions on the wire are constant, once the wire has been stretched or otherwise deformed the wire will have an undesirable amount of sagging. To avoid this problem, cutting wire systems normally include a feature such as a plumb weight so as to maintain a constant tension on the wire, even after it has been stretched past its elastic limits. However, even with the plumb weight, once a cutting load is applied to the wire, the wire's earlier deformation still leads to instability and decreased cutting precision. Thus, it is important to manage tool loading pressures during system operation so that the loading pressures are within the limits of the cutting wire's elastic stability.
Accordingly, what is needed is a wire cutting system that can continuously detect the precision of cuts being made and modulate the cutting wire's feed rate so as to maximize cutting performance and to extend the working life of the cutting wire.